Observational field studies reveal wild birds responding to early-life stresses with resilience, plasticity, and intergenerational effects

Abstract

An extensive experimental literature documenting negative impacts of early stresses such as food deprivation, elevated corticosterone, and brood enlargement on numerous morphological, physiological, and behavioral traits of adult birds has left the impression of generalized developmental vulnerability to stress in birds. However, descriptive studies of wild populations, most of them recent, are indicating that natural stresses can sometimes elicit resilience or flexible variation in adult life history traits, and that such plasticity can neutralize impacts of stress on fitness. Experiments, almost entirely in captivity, were not designed to detect such effects, and most were not suited for this purpose in that treatments did not mimic natural stresses, effects were seldom measured over the lifespan, and fitness consequences were rarely assessed. Future research needs to take into account that early stresses can elicit positive developmental responses, that the direction of effects of stresses can depend on their magnitude, and that a deficit in one fitness component can be compensated by modification of others. Different styles and types of research can shed more light on avian developmental plasticity by characterizing natural stresses more precisely, measuring their effects on diverse variables including fitness over the lifespan, conducting field experiments, and adopting a life history framework.